The reason I was messing around with Doom's RNG was I was studying how early
versions of Doom performed random pitch-shifting of sound effects, a feature
that was removed early on in Doom's
history. By fixing the
random number table and replacing the game's sound effects with a
sine wave, one second long and tuned to middle-c, I was able to determine
the upper and lower bounds of the pitch shift.

I'm pleased with the final result. It's the most significant bit of C code I've
ever released publically, as well as my biggest Doom hack and the first time
I've ever done any audio manipulation in code. There was a load of other notes
and bits of code that I produced in the process. I've put them together on a
page here: More than you ever wanted to know about
pitch-shifting.